THE PROPERTIES OF ACICULAR PARTICLES OF (GAMMA-FE2O3)X(FE3O4)1-X

It is known that acicular particles, initially of Fe//3O//4, which have been partially oxidized, show anomalous properties e. g. in the variation of H//c with composition. It is shown that these can be explained by considering the particles to comprise an inner core of Fe//3O//4 with an outer layer of gamma -Fe//2O//3. Owing to the large change in volume which occurs on oxidation, these mutually stress each other. Over a certain range of composition, the stress field interacts with the magnetization to increase H//c, and it is also responsible for H//c increasing with time after the oxidation process. A similar situation applies to partially reduced gamma -Fe//2O//3.